In the field of handling bulk material such as agricultural fertilizer, grains, forage and the like, the side dump box assembly finds utility. Typically, the side dump box assembly is mounted on a truck or trailer bed and includes a support frame and a side dump box pivotally assembled to the support frame for elevated rotation about an axis parallel to and in proximity to an upper side edge of the dump box. Means such as hydraulic cylinders are provided for rotatably elevating the dump box above the support frame to pivot it about the dumping axis and accomplish the dumping operation. See, for example, U.S. Pat. No. 3,633,971 to Berky.
The material in the dump box is transferred to a receiver, such a spreader, located alongside the truck or trailer accommodating the dump box. A purpose of the dump box assembly is to locate the dumping edge of the dump box over the receiver. It is thus necessary that the dumping edge of the dump box extend laterally beyond the bed of the truck or trailer and at an elevation above the receiver during dumping. Careful positioning of the receiver relative to the dump box is necessary. The receiver must be located in close proximity to dump box assemblies of the prior art due to inherent limitations in the elevations and lateral displacement of the axis of rotation of the dump box. It is desirable, therefore, in a dump box assembly to have means provided for elevation and lateral displacement of the axis of rotation of the dump box to alleviate the necessity of tediously positioning the receiver in proper proximity to the dump box assembly and for more complete filling of higher and/or wider receivers. At the same time, it is desirable to limit the degree of lateral travel of the center of gravity of the dump box assembly whereby it is maintained in a stable range over the center line of the bed supporting the dump box assembly.